1. Field of the Invention
The present invention relates to beryllium-copper which contains at least Be and Cu and has plastic strain added thereto, a method for producing the beryllium-copper, and an apparatus for producing the beryllium-copper.
2. Description of the Related Art
Precipitation type copper alloy containing beryllium (Be) (hereinafter referred to as beryllium-copper) has been generally and widely used as a high strength spring material, a conductive material, or the like.
When beryllium-copper is cold processed (at ambient temperature) by casting, rolling, pressing, and the like (hereinafter referred to as casting processing or the like), work hardening advances remarkably. Therefore, it is difficult to process beryllium-copper into desired dimensions by performing casting processing or the like once.
Therefore, beryllium-copper is generally hot-processed (at high temperature) by casting processing or the like (for example, refer to Japanese Patent Publication No. 2088889 (claim 1, FIG. 1, and so forth)).
To be specific, beryllium-copper is processed under processing conditions of specific processing temperature (600° C. to 800° C.) a specific processing speed (3.3×10-5S-1 to 1×10S-1), a specific amount of working strain (0.20 or larger), and the like, and uniform and fine crystal grains are formed into beryllium-copper.
However, in the conventional technology, since a crystal grain is micronized by utilizing dynamic recrystallization which is induced by performing hot processing (at high temperature) to beryllium-copper, the crystal grain of beryllium-copper has only been micronized down to in the order of 30 μm.
Here, if considerable strain can be applied to beryllium-copper, there is a possibility of gaining a fine crystal grain by an HPT (high pressure torsion) method, an ECAE (equal channel angular extrusion) method, an ARB (accumulative roll bonding) method, and the like, which however has not been appropriate for industrial use.
The HTP method is a method where a large shear deformation is made in a small disc-shaped test piece by torsional deformation while applying large pressure to the test piece. Also, the ECAE method is a method where a material is repeatedly passed through dies which have a constant cross sectional area and a bend portion so as to add a simple shear deformation to the bend portion.
To be more specific, with the HPT method, because an amount of strain varies depending on a distance from the center of a disc-shaped test piece (a position in the radius direction), uniform crystal grains cannot be obtained. With the ECAE method, since life of dies is short, it is not appropriate for mass production. Moreover, the ECAE method is not appropriate for continuous production of large-sized structural materials in an industrial scale either. With the ARB method, as work hardening is large, it is difficult to process a material under a massive pressure for each pass. Further, with the ARB method, bonding is prevented as an oxide film is created by active elements of Be and the like.
Also, in the method stated in Patent Document 1, since beryllium-copper is hot-processed (at high temperature), an oxidized scale is generated in beryllium-copper, and work need to be done to remove the generated oxidized scale.
Here, a method which can be considered is the one for processing beryllium-copper at specific processing temperature for specific processing time (for example, temperature of 300° C. and time of 30 minutes or shorter) with which an oxidized scale is not generated in beryllium-copper and age hardening of beryllium-copper does not progress. However, because beryllium-copper should be processed while strictly controlling the processing time and processing temperature, it is difficult to put this method into practice.